1. Field of the Invention
The present invention relates to memory devices, and more particularly to dynamic adjustment of a refresh interval of a memory device to minimize the average refresh power of the memory device.
2. Description of the Related Art
Memory devices, such as, dynamic random access memories (DRAMs) include a wide variety of applications. The use of DRAM memory is extremely attractive to many such applications due to its high density and low power access. When used in applications, the power needed to refresh the DRAM becomes a significant part of the standby power of the system. It is well known that the frequency of refresh needed to guarantee stored data integrity is a function of temperature and operating voltage (to the extent that the stored charge is a function of operating voltage). Conventional art usage of DRAM memory ensures refresh rates corresponding to the anticipated worst case values of these conditions. This results in refresh rates much higher than needed for a majority of actual operating conditions.
Hardwired refresh controllers, as used in prior art computer systems, generally lack the flexibility to alter this conventional art approach. However, in many applications the refresh of DRAM may be controlled via more sophisticated refresh controller logic embodied either as special purpose hardware or as a task running on a control or signal processor invoked by a timer event. The approach using a program on an embedded processor is attractive since the approach permits high priority processing to use the memory by deferring refresh while ensuring that the overall refresh rate remains within specifications. Both of these approaches provide flexibility to dynamically adjust the refresh rate, but still do not provide refreshing based on need. Instead, additional unnecessary refreshes are employed which can be expensive in terms of power dissipation, especially in systems, such as mobile systems, which employ batteries.
Therefore, a need exists for a system and method for reducing refresh rates of memory devices. A further need exists for sensing what is a minimum necessary value under current environmental conditions and manufacturing variations to initiate a refresh operation of the memory device.